DESCRIPTION (Applicant's Abstract): When viewed in social context, early vocal behavior is an instrument of learning. Through the activity of vocalizing and observing the reactions of others, infants acquire an understanding of the contingencies that structure communicative interaction. The purpose of the proposed research is to elucidate the role of the receiver in human vocal learning. Adapting methods used successfully in studies of animal communication, the proposed research will address social contributions to vocal learning by assessing adult responses to playbacks of infant behavior. In Project 1, playbacks of infant behavior will be used to specify the acoustic determinants of maternal responses to prelinguistic vocalizations. To validate and extend the initial findings, additional playback studies will focus on the effects of perturbations of vocal characteristics. Natural and synthetic vocalizations will be used to model the changes in vocal behavior exhibited in Down syndrome infants that create differences in the development of social response which may facilitate communicative dysfuntion. In Project 2, a second playback series will assess the influence of experience on responsivity to infant sounds. Follow-up studies will assess the effectiveness of training on the acquisition of experienced maternal patterns of responding. Taken together, these studies explore the origins of communicative competence as emergent from the system of sender and receiver, and will increase our knowledge of the contingencies that frame communicative interaction in both typically-and atypically developing populations.